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Leak testing in automotive parts need speed, accuracy and dependability |
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Radiators, fuel tanks, mufflers, oil filters and air conditioners are some of the automotive parts that must be checked for leaks. Additionally, the leak rate specifications have become much tighter during the past decade. US State and federal standards restricting emissions of chlorofluorocarbons, exhaust and fuel vapors have forced automotive assemblers to radically tighten leak rate specifications for parts such as fuel tanks, fuel rails, brake lines, torque converters and air-conditioning compressors. There are several technologies for performing leak tests on various automotive parts. Few of them are:
Transmission Castings:
Transmission castings are usually tested with air using a mass flow instrument. The leak rate specification is approximately 5 standard cubic centimeters per minute (sccm). The test system is manually loaded, semiautomatic setup with quick-change tooling, or a dedicated, fully automatic with robotic parts handling.
Radiators and Heater Cores:
Both the heater core and the radiator carry coolant but their leak rate specifications are different. Heater core has 0.5 to 1 sccm is usually tighter than for the radiator which is 4 to 5 sccm. The reason is that a heater core is located in the passenger compartment, while the radiator is in the engine compartment.
Fuel Injectors:
Fuel injectors are among the most difficult automotive assemblies to test for leaks. The test volume is less than 0.1 cc, and the cycle time is less than 2 seconds. Temperature compensation is necessary when testing fuel injectors, which can fluctuate in temperature during testing. They are usually welded with a laser. If tested soon after assembly, they may still have some residual heat. Injectors can also become warm due to the high pressures at which they are tested. Some injectors are tested at pressures of 100 psi or more.
Fuel Rails:
Fuel rails are usually tested with a tracer gas, such as hydrogen. Like many auto parts, the leak rate specification for fuel rails has become tighter during the past few years. Today, the leak rate limit for a fuel rail is less than 0.5 sccm at a test pressure of 100 psi.
Air-Conditioning Components:
Evaporators, condensers and other air-conditioning components carry gas & are therefore tested to a higher leak rate specification 0.00008 to 0.00002 atmospheric cubic centimeters per second (accs)�than auto parts that carry liquids. These components are usually tested using helium or hydrogen
Fluid Reservoirs:
Every engine compartment contains several plastic reservoirs for various liquids, such as power steering fluid, coolant, and windshield washer fluid. Detecting leaks in these assemblies can be challenging because the plastic expands and contracts with positive or negative pressure. Depending on cycle times, bottles are tested with air using a mass flow or pressure decay system. The pressure decay method works better with reservoirs that have thick, rigid walls. The mass flow technique is better for reservoirs with thin, bendable walls.
Wheel Rims:
The leak rate specification for wheel rims is not terribly stringent, perhaps 0.0003 accs at a test pressure of 40 psi. This application requires a high-throughput system, which can be loaded manually or automatically.
Air Filters:
Air filters especially carbon-filled models pose a unique challenge for leak testing equipment. The carbon acts like a sponge, creating a part that takes an extremely long time to stabilize for pressure decay monitoring
Gas Cap:
Like the heater core, the gas cap is �on the border� between needing a pressure decay system or a helium mass spectrometer system
Fuel Tank:
With a leak rate specification of 0.00001 to 0.0001 accs, fuel tanks are tested using a helium mass spectrometer system. Depending on the size of the tank, test time ranges from 45 to 65 seconds. The challenge with testing fuel tanks is that they can only withstand a positive or negative pressure differential of 1 or 2 psi without bursting or buckling. To prevent that, the tank and the chamber must be evacuated simultaneously.
(Extracted from an article by John Spirovi) |
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